Sheriff: Colo. Gunman Planned to Hurt More People

Authorities say an 18-year-old who wounded a fellow student before killing himself at a suburban Denver school entered the building with a shotgun, a machete and three incendiary devices in his backpack, and had ammunition strapped to body.

Arapahoe High School in Centennial, Colorado (CBS 4 Denver)

Arapahoe County Sheriff Grayson Robinson says Karl Pierson was motived by retaliation against a faculty member — probably a librarian — when he opened fire Friday at Arapahoe High School.

The sheriff says it appears the school librarian was the initial target but that Pierson planned to hurt multiple people.

Robinson says the librarian is leader of the speech team and Pierson was a member. He says the librarian disciplined Pierson in September but didn't kick him off the team.

Robinson also says Pierson bought the shotgun legally Dec. 6 at a local store.